An idiom characterizes a society, and when you ignore the idiom, you are very likely ignoring the whole social fabric that could make a meaningful character. You can’t cut characters off from their society and say much about them as individuals. You can’t say anything meaningful about the mystery of a personality unless you put that personality in a believable and significant social context. And the best way to do this is through the character’s own language. When the old lady in one of Andrew Lytle’s stories says contemptuously that she has a mule that is older than Birmingham, we get in that one sentence a sense of a society and its history. A great deal of the Southern writer’s work is done for him before he begins, because our history lives in our talk. In one of Eudora Welty’s stories a character says, ‘Where I come from, we use fox for yard dogs and owls for chickens, but we sing true.’ Now there is a whole book in that one sentence; and when the people of your section can talk like that, and you ignore it, you’re just not taking advantage of what`s yours. The sound of our talk is too definite to be discarded with impunity, and if the writer tries to get rid of it, he is liable to destroy the better part of his creative power.
From Flannery O’Connor’s lecture “Writing Short Stories.” Republished in Mystery and Manners.